The present invention relates to a hot-wire air-flow meter, and particularly to a hot-wire air-flow meter for automobile engines in which a throttle valve for controlling the flow rate of air sucked into the engine is integrated.
An internal combustion engine for automobiles has a fuel supply system comprising a fuel supply line and an air induction line. In the fuel supply system, air purified by an air cleaner is introduced into the engine through a passage. The passage is provided with a fuel supply port, a throttle valve for controlling the flow rate of air flowing into the engine and a hot-wire air-flow meter for measuring the airflow rate. In a conventional internal combustion engine for automobiles, there is a relatively large distance between the throttle valve and the air-flow meter. Namely, the former is arranged near a collector inlet of an intake manifold, and the latter immediately downstream of the air cleaner. When installing them in an automobile which has a cramped engine compartment, it is necessary to integrate the hot-wire air-flow meter and the throttle valve in order to improve mounting easiness and space and reduce the cost of the fuel supply system. FIG. 1 of Japanese Laid-open Patent Application No. 55-104718 shows an integrated flow meter and throttle valve which is mounted on the collector of the intake manifold.
Further, when the space within the engine compartment is limited, an upstream side of the air-flow meter and a downstream side of the air cleaner are communicated by means of a bent duct, as disclosed in Japanese Laid-open Patent Application No. 57-103016. The bent duct, which is bent immediately upstream of the air-flow meter, causes turbulence; therefore in the prior art there is provided a rectifier between the air-flow meter and an air cleaner in order to rectify the turbulence of the air flow.
Turbulence raises the problem that the output voltage of the air-flow meter with respect to the volume of air becomes high with the integrated type of meter, compared with the output voltage of a separate meter in which the air-flow meter is separated from the throttle valve with a relatively large distance, as above-mentioned. Further, the waveform of the output voltage of the integrated meter shows large pulsations compared with the separate meter. Therefore, it is difficult for the hot-wire air-flow meter accompanied by the turbulence to detect the real value of the air flow rate.